1. Field of the Invention
This invention relates to an image forming apparatus such as a copier or a printer using the electrophotographic method or the electrophotographic recording method, and particularly to an image forming apparatus using a two-component developer.
2. Related Background Art
In conventional image forming apparatuses of the electrophotographic type for effecting chromatic colored image formation, a two-component developing method including a developer container; a nonmagnetic toner and a magnetic carrier are used.
The two-component developing method, as compared with the other presently proposed developing methods, has such advantages as the stability of image and the durability of the apparatus. On the other hand, the deterioration of the developer by long-term use, particularly the deterioration of the carrier, has been unavoidable and therefore, it is necessary to do the work of interchanging the developer with the long-term use of the image forming apparatus.
Some countermeasures for this problem have heretofore been proposed.
For example, according to Japanese Patent Publication No. 2-21591, in a developing apparatus for an electrophotographic copier provided with agitating means for agitating a carrier and a toner, and a developing roller which is a developer carrying member for supplying the developer agitated by the agitating means to a photosensitive body which is a latent image bearing member, a carrier supplying (replenishing) apparatus and a toner supplying apparatus are separately or integrally provided above the agitating means, and a developer overflowing portion is provided on the side wall of the housing of the developing apparatus and therefore, a fresh developer can be supplied little by little by the above-mentioned supplying apparatuses and be discharged from the above-mentioned overflowing portion, and the characteristic of the developer in the housing of the developing apparatus can be maintained constant and as a result, the quality of image of copies can also be maintained constant. Also, the developer in the housing of the developing apparatus which has become old is sequentially automatically discharged from the developer overflowing portion, and this eliminates the necessity of the cumbersome developer interchanging work of detaching the developing apparatus from the copier, taking out the old developer in the housing of the same apparatus and replenishing (refilling) the housing with a fresh developer, and thereafter mounting the developing apparatus again, and moreover the scattering of the developer is prevented and this is hygienic.
That is, the deteriorated developer (carrier) is gradually replaced by a fresh one, whereby the progress of the apparent deterioration of the carrier is stopped and the characteristic of the developer as a whole is stabilized. Thereby, the work of interchanging the developer is made unnecessary and the maintenance property is improved.
Also, a construction in which this system is combined with the construction of a rotary type developing apparatus is proposed in Japanese Patent Application Laid-Open No. 9-218575, and according to this, this rotary type developing apparatus is provided with developer supplying means for replenishing a developing device with a necessary developer. Also, any excess developer in the developing device is discharged by the utilization of a change in the acting direction of gravity by the rotation of a rotary member. By thus utilizing a movement peculiar to the rotary member, the excess developer can be discharged by simple structure.
Besides these, various systems which do not resort to the rotary type developing apparatus have been proposed, and for example, in Japanese Patent Application Laid-Open No. 10-63074.
On the other hand, in recent years the market of full color copiers and printers has been enlarged, and among various functions being required, for example, many image forming apparatuses of the tandem type having a plurality of photosensitive drums disposed for effecting multiplex transfer have been produced to provide high productivity, and seem to become one of the mainstreams of the market in the future.
In the image forming apparatus of the tandem type, however, developing apparatuses of respective colors are fixedly disposed for respective photosensitive drums, and the simple structure as proposed in Japanese Patent Application Laid-Open No. 9-218575 could not be utilized. Therefore, in the image forming apparatus of the tandem type, to adopt the method of gradually replacing the developer with a fresh one, it has been necessary to adopt a complicated construction as shown in Japanese Patent Application Laid-Open No. 10-63074. This also holds true in image forming apparatuses for forming monochromatic images.
That is, according to the prior art, in monochromatic image forming apparatuses and full color image forming apparatuses of the tandem type yielding high productivity or of various constructions which do not adopt the rotary type developing apparatus to make the most of various features, if an attempt is made to gradually automatically interchange the developer to thereby increase the maintenance property, the complication of construction has been conversely yielded, and this has led to the rise of the cost of the main body of the apparatus.
It is an object of the present invention to provide an image forming apparatus which enables a carrier in a developing device to be automatically interchanged little by little.
It is another object of the present invention to provide an image forming apparatus which enables a carrier collected from a developing device to be carried into a cleaning container.
It is still another object of the present invention to provide an image forming apparatus comprising:
an image bearing member bearing an electrostatic image thereon;
developing means for developing the electrostatic image on the image bearing member by a developer having a toner and a carrier;
transferring means for transferring a toner image on the image bearing member to a transferring material;
cleaning means for cleaning any residual toner on the image bearing member after the transfer; and
carrying means for carrying the developer in the developing means to the cleaning means.
Further objects of the present invention will become apparent from the following description.